This invention relates to the field of ink jet printing devices, and more particularly to a formed traveling wave guide for an orifice plate for use in an ink jet printing device and a method for its manufacture.
In a typical ink jet printing device, a liquid reservoir is utilized to contain a printing ink with a multi-jet orifice plate being secured to the bottom of the reservoir. The orifice plate contains a plurality of very small diameter holes spaced along its length, usually in sets of rows. During operation, the ink under pressure is forced through these orifices and forms pendulant filaments which ultimately break up into streams of drops. It can be appreciated that in order to obtain uniform printing, these streams of drops must be of uniform size and spacing. In order to do this, means are usually provided for stimulating vibration of the orifice plate, either directly or indirectly, to cause motion in the ink supply which induces pressure waves along the filaments extending from the orifices so that drops of uniform size and spacing are produced.
The main problems associated with stimulating the orifice plate are spurious vibrations, undesired reflections, and loss of acoustical energy along the orifice plate. Many of these problems stem from the manner in which the orifice plate is secured to the ink manifold in an ink jet printing device. Common practice in the art has been either to solder or epoxy the orifice plate to the bottom of the manifold. However, in epoxying the plate to the manifold, it is very difficult to apply uniformly the adhesive bead of epoxy. This results in slight distortions in the orifice plate when it is pressed against the manifold and variations in the distance of separation between the two. These distortions and variations result in spurious vibrations and/or loss of acoustical energy.
Soldering also has drawbacks in that distortions, caused by the necessary heating to solder the connection, are introduced into the orifice plate. Since orifice plates are quite thin, they are easily warped or distorted. Such distortions are undesirable because they change slightly the relative position of the orifices from an otherwise straight alignment and result in misalignment problems with the charging and deflection mechanisms in the printing device and ultimately in poor quality printing.
Sweet et al, U.S. Pat. No. 3,373,437, disclose a unitary orifice plate and ink supply manifold construction of a rectangular, channel-shaped cross section and teach that either the wall containing the orifices or an opposite wall may be vibrated to induce uniform drop formation. However, because of the direct connection of both of these walls to the relatively thin sidewalls, it is apparent that vibrations will be induced in the sidewalls causing spurious vibrations in the ink supply in the manifold and adversely affecting the uniformity of filament lengths. This irregularity of filament lengths adversely affects printing quality.
Several attempts have been made in the art to overcome the problems of bonding orifice plates to ink supply manifolds. For example, Kenworthy, U.S. Pat. No. 4,107,699, teaches use of a trenched orifice plate having a thin central section with thicker sections on either side forming acoustical barriers to undesired vibrations. However, fabrication of such a trenched plate requires several steps including photofabrication, plating, and/or etching of the structure. Paranjpe et al, U.S. Pat. No. 4,146,899, teach an orifice plate having sidewalls which are backed by acoustically absorbent material to prevent the propagation of spurious vibrations from the orifice plate to the sidewalls. However, the effectiveness of that structure in preventing undesirable vibrations is quite dependent on the nature and quality of the bonding and surface to surface contact of the sidewalls with the backing layer.
Accordingly, the need still exists in the art for a structure which is simple to manufacture and which contains the acoustic energy applied to the orifice plate within it independently of, and substantially unaffected by, the bond between the orifice plate and ink supply manifold.